In flat-bottomed silos for storing grains or the like, emptying the last portion of the product in the silo presents a problem. As long as the remaining volume is great, gravity operates to empty the silo. But, toward the end of the emptying process, when there is very little product left in the silo, the remaining products from a sloping pile which will not empty from the silo merely through the action of gravity. The remaining volume is not necessarily negligible, as in some silos it can reach several tons which will not slide out of the silo.
To accomplish complete emptying, apparatus for sliding and forcing this remaining mass towards the exit opening of the silo must be provided.
Conventional systems provide for injection of pressurized air under the silo floor.
According to a first known system, the silo floor has openings formed by slits in a metal sheet which forms the silo floor. The metal on one side of the slit is moved to create outlets in the metal floor. However, this process is disadvantageous in that it cannot be used for large silos, e.g., where the length of the silo sides or the diameter of the silo is in the range of a few dozen meters, because in such cases, substantial energy is necessary to move the metal on one side of the slit.
According to a second known system, casings are provided alternating between flat sections and hollow ribs at the bottom of the silo. The casings have air outlets on each of their sides, and each hollow rib forms a ventilating duct. This known system, however, is disadvantageous in that grains tend to rub against the floor sections located between adjacent ribs, requiring much energy to overcome this friction. Furthermore, this system is disadvantageous in that the airstream at the outlets flows obliquely in relation to the forward feeding direction of the grains, thus resulting in inefficient use of energy.
In order to reduce energy loss, it is possible to force the air through some ventilation ducts and to cause emptying by intermittent operations. In conventional systems, emptying is achieved by forcing air through two ventilation ducts defining an emptying channel. However, in such systems, most of the air escapes via the sides of the empty adjacent emptying channel.